Atmospheric analysis by open-path Fourier-transform infrared (OP/FT-IR) spectrometry has been possible for over two decades but has not been widely used because of the limitations of the software of commercial instruments. In this paper, we describe the current state-of-the-art of the hardware and software that constitutes a contemporary OP/FT-IR spectrometer. We then describe advances that have been made in our laboratory that have enabled many of the limitations of this type of instrument to be overcome. These include not having to acquire a single-beam background spectrum that compensates for absorption features in the spectra of atmospheric water vapor and carbon dioxide. Instead, an easily measured â€œshort path-lengthâ€ background spectrum is used for calculation of each absorbance spectrum that is measured over a long path-length. To accomplish this goal, the algorithm used to calculate the concentrations of trace atmospheric molecules was changed from classical least-squares regression (CLS) to partial least-squares regression (PLS). For calibration, OP/FT-IR spectra are measured in pristine air over a wide variety of path-lengths, temperatures, and humidities, ratioed against a short-path background, and converted to absorbance; the reference spectrum of each analyte is then multiplied by randomly selected coefficients and added to these background spectra. Automatic baseline correction for small molecules with resolved rotational fine structure, such as ammonia and methane, is effected using wavelet transforms. A novel method of correcting for the effect of the nonlinear response of mercury cadmium telluride detectors is also incorporated. Finally, target factor analysis may be used to detect the onset of a given pollutant when its concentration exceeds a certain threshold. In this way, the concentration of atmospheric species has been obtained from OP/FT-IR spectra measured at intervals of 1 min over a period of many hours with no operator intervention.

Abstract. We have reinvestigated [sup 13]CH[sub 3]OH as a source of far-infrared (FIR) laser emission using a CO[sub 2] laser as a pumping source. Thirty new FIR laser lines in the range 36.5 mu m to 202.6 gm were observed and characterized. Five of them have wavelengths between 36.5 and 75 mu m...

The rotational spectrum of the weakly bound complex OCS CO2 has been measured using a pulsed beam Fourier transform microwave spectrometer. The rotational constants of the major isotopomer are A=4454.606 MHz, B=1517.778 MHz, and C=1129.666 MHz. The molecule is planar with a â€˜â€˜slipped...

The matrix isolation technique is traditionally used to investigate the properties of the matrix-isolated species themselves or to solve some special questions of the theory of defects in solids. We showed here that the optical spectroscopy of real matrix-isolated molecules can be successfully...

We present the first study of the influence of line mixing among CO2 lines on the remote sensing retrieval of atmospheric carbon dioxide. This is done in the bands near 1.6 and 2.1 Î¼m which have been retained by the Orbiting Carbon Observatory (OCO) and Greenhouse Gases Observatory Satellite...

Two-dimensional correlation spectroscopy was used to study the composition-dependent spectral variations of the CH-stretching bands of N,N-dimethylformamide (DMF)-water mixtures with XDMF ranging from 0.98 to 0.60. By a detailed correlation analysis of the spectral changes of the CH- and...

Infrared spectra of supersonic jets of carbon dioxide seeded in helium are reported: Features assignable to clusters were observed for the Î½2, Î½3, Î½1+Î½3, and 2Î½2+Î½3 bands. A detailed study was made of the Î½3 band, from which it was concluded that the clusters do not adopt...

Editorial. Traces the historical development of commercial infrared spectroscopy. Description of spectrometers; Advent of the Fourier transform-infrared spectrometer; Research on near-infrared portion of the spectrum.